This project will follow 78 Very Low Birth Weight (VLBW) infants previously enrolled in a R21 grant through the age of 4 years. The data gathered over 6 weeks of the NICU stay includes multiple factors that potentially could alter the gut micro biome, such as prenatal and postnatal events and illnesses, amount of human milk received, weekly means of cytokines, chemokine's, growth factors and secretory Immunoglobulin A in the milk, and weekly levels of fecal calprotectin. Stool samples have been preserved for analysis of the micro biome in the current study. Micro biome species and diversities will be measured in the laboratory of Dr. Jack Gilbert at Argonne National Lab using state of the science deep sequencing and amplification of microbial sRNA genes. The micro biome will again be measured in stool samples from these children at the ages of 2 and 4 years. Relationship between the pre and postnatal factors, human milk volume and immunobiology, fecal calprotectin levels and the very early micro biome will be analyzed. The predictive power of the VLBW infant gut micro biome for determining later childhood micro biomes will be analyzed prospectively. The relationships between micro biomes across time and later growth, development and health will be determined. VLBW infants are at risk for both early and later health effects, and the role of the micro biome in these effects will be measured for the first tim in this prospective study.